Process for making styrene from methyl phenyl carbinol



Patented Apr. 30, 1946 PROCESS FOR MAKING STYRENE FROM METHYL rnmvrr. CARBINOL Leland C. Shriver, South Charleston, W. Va., assignor to Carbide and Carbon Chemicals Corporation, a corporation of New York No Drawing; Application September 23, 1943, Serial No. 503,528

9 Claims. (Cl. 260-1569) That phenyl methyl gcarbinulmay be dehydrated to form;styrene"is'i'welljknown, and a" number of catalystslshavelgbeen roposed for this reaction it has 'th, withstyrene, a

reaction. In carryin been observed th dimer of styrene'an in ss'er amount, an 1mpurity having a point lying very close to that of styrene are invariably formed. Depending upon such factors as the temperature, the catalyst and the feed rate, ifzthe carbinol is added during the reaction, the efflciency losses due to formation of thedimer may run as high as 3.5 to 15 per cent; Then, too, the ether of phenyl methyl carbinol'will be formed and appear in the reaction product bysupplying carbinol during the course of the-reaction at a feed rate so high that incomplete dehydration results. Although further dehydration of this ether to styrene takes place in the liquid phase only slightly more slowly than in the case of the carbinol, its separation from the reaction product before recycling is difficult. Both the ether and the dimer are very high boiling, with the dimer boiling about 20 C. above the ether.

In carrying out the dehydration in the liquid phase, the operation must be shut down from time to time to permit the removal of high boiling residues which accumulate in the reaction mixture. These high boiling residues result from the polymerization of styrene which is always present in the reaction mixture, and the need for shut-downs is aggravated also by the formation of the high boiling liquid dimer of styrene. Thus, at best, the liquid phase dehydration. of styrene cannot be operated continuously. Under some conditions the accumulation of polymeric high boiling residue may be so large as to constitute an important percentage of the styrene which is formed, and as a consequence of this styrene polymerization the actual eiiiciency of the liquid phase dehydration is lowered correspondingly. Then. too, it is necessary to resortto a reaction expensive construction, in which the ratio of vessel of complicated design and correspondingly heating surface to liquid heated is very large, in order to keep the amount of hot liquid in the reaction vessel at a minimum and maintain a low styrene-polymerization loss.

Of equal, if not greater, importance from the standpoint of purity of the styrene is the ,difilculty of eliminating the impurity boiling close to styrene. The boiling pointlies so closethat its separation from styrene by distillation is not practicable. The amount of this difficultly removable impurity may vary widely with different catalysts but with none of the catalysts heretofore suggestedhas it been possible to obtain both a high' activity and a high quality styrene.

I have discovered that styrene of high purity may be obtained by conducting the dehydration of phenyl methyl carbinol in the vapor phase over a titania catalyst. Although good results are obtainable with a number of grades of titania, it is desirable to employ titania of a high grade of purity for best results. The amount of dimcultly separable impurity present in the high quality styrene produced according to the invention seems to be dependent at least to some extent .upon the purity of the titania catalyst employed. For instance, an improvement in the quality of the styrene from about 99.2 per cent to" upwards of 99.6 per cent is eflected progressively on going from the pigment grade to the technical reagent grade to the so-called C. P. anhydrous grade of titania. Using technical grades of the titania the purity oi the styrene obtained after separating from the crude reaction product the high boiling dimer as well as any unreacted carbinol and its ether, may run styrene having a purity of about 99.5 to 99.7 per cent, by weight, or better may; be'obtained. The

loss of efficiency due to: dimer formation seems not to exceed about 2.5 to 6 per cent.

The titania catalyst may be used in supported form or in pellets. Typical of suitable inert supporting materials are crushed sandstone, silica filter stone and ceramically-bonded, iused aluminum oxide. For instance, the fused aluminum oxide may be wetted with water, titania powder amounting to about 10 to 15 per cent of the oxide then sprinkled on, and the catalyst and support measuring less than inch in the largest dimension. On the larger side, however, good production ratios may be obtained with pellets measuring up to inch in one or more dimensions, for

dried at 150 C. Because of the tendency of the 5 instance, production ratios of about 400 to 600 ti p w r t t ofi, it is possible that only grams per liter per hour using pellets x 1; inch. about 5 t 8 Pe ce eventually remains- The Little if any improvement in production ratios v y of the itania powder a e increased seems to result on going from a supported cataabout ey treating i with hot aqueous lyst to catalyst pellets larger than inch. On sulfuric ac d (10 per cent). followedby thoro h 10 the other hand, production ratios of 800 to 1100 V 8 Wlth Water remove the h grams per liter per hour are obtainable on going tits-ma is applied to the support ,Wlth tltama to a pelleted catalyst of about? inch diamsupported on 4 x 6 mesha n eter x1; inch size, the improvement amounting fused aluminum oxide production ratios of 400 to approximately 100 per cent over the inch to 650 grams of ityrene per .hter of catalyst per pellet. These comparative values are for a catahour may obtamqd' coltslderabty mgher lyst bed. approximately 1 inch in diameter and duction ratios are possible with the tltanium cata- 12 to 15 inches long using a feed containing lyst in pellet form. In pelleting the catalyst. titam dj xid wde of a hemjc u ur anh about per cent acetophenone. With catalyst e r c a y p e beds 4.5 to 20 feel long the improvement with the drous grade is thoroughly wet with water and 20 n t d t 1 t th m h 1 is the resultant paste dried at 130 to 150 c. The P6 e e a ys e e s ze even dried cake is powdered and then pelleted in a. mm marked, pmduc m'iwsebove pelleting machine or other suitable device for grams per liter per hour bemg conslstently making pellets. At this stage the pellets are tainable, and even reaching as high as 3400 grams rather weak, and although they may be screened, per hter per they dust somewhat freely in service in the vapor For e most part the deslrable temperatures phase reaction. The pellets are then fired in an of operatlen are found between and electric furnace at a temperature of at least 800 Usually 1t 15 unnecessary to use temperatures C., whereupon they become very strong and suitf above At temperatures or able mechanically. After the pellets have been to 220 e reduced P e y be fired they may be subjected to an activation step g il to esslst i g zstgletgazrgnol. by immersion in boiling nitric acid (18-20 per 1% mpera mes Tom a cent concentration) for a period of about 90 minm be e p oy und c t n d o s. for lites. Following the acid treatment the pellets Instance, If i e d t ob ain an economical are ready for charging to the converter aft production ratio with feed rate so high as to tend thorough washing with water and drying at about to esult t0 Incomplete y ation. 130 to 150 C. In addition to nitric acid, hydro- The purity of the styrene obtainable acco chloric acid, phosphoric acid or sulfuric acid may to the Process thls invention is n t adversely be used for the acid treatment. Between 800 affected y he presence of acetophenone in the and 1000 0., there appears to be a point i t 40 feed; at least not in amounts up to at least 25 heat treatment which results in a shrinkage of P a th y l tlff tle ieeidto'lhus the process the pellet. The pellets are harder and denser, 15 P 1011 y We a -D 6 opera 8 n he and a inch pellet which will retain its size when e yl methyl a l o d y h d ofired at 800 C. may shrink to a' diameter of about te tt l 0f acetophenone d c ta ng subr'i; inch when fired at temperatures from about 5 en la amounts 0 unchanged tophenone. 00 t 1100 Q These denser, harder pellets do The acetophenone passes substantially unchanged not seem to be as readily activated by nitric acid throlggh the ph yl m hyl carbinol converter and as those roasted t 00 C" even using the may erecovered from the styrene product. centrated 70 per cent grade of nitric acid. They h u e Ph nyl m hyl oarbinol is a mamay be suitably activated, however, using aqueous tellal Whlch 1S felrly readily de ydrated, it seems phosphoric acid of 20 per t concentration probable that a number of substances exhibiting The denser. harder pellet h t advantage t t dehydrating characteristics would serve to catadusting of the catalyst, particularly during a lf tIhe reeetioh- The y the P d ction racharging operation, is largely eliminated, and for tios and the p rity of the styr P d ced with this purpose a roasting temperature of about 1000 a number of materials :vhich iave previously been C i preferred, suggested are given 11 Ta 1e A. The phenyl In general, the smaller the pellet size the better methyl carbinol used in these runs was a mixture the production ratio, although for mechanical am g from about 5 to 20 per cent acetoreasons it may not be feasible to go to pellet sizes D non Table A Styrene, Description oi material Yield "2233? 1: 3m? g gg gg P l w. P z "c. Tungstlc trioxlde (green), 20% on support $5. 8 428 30. 84 29 250460 Aluminum phosphate, 20% on support 62. 6 249 -3l. i4 98. 81 245-261 3x21031132 i i cm inch) 5 .7 305 -a0. 91 99. 35 Slim 1X50 oxide, 15% oi'i'ai'iii'per't' IIIII 84.4 452 50.88 99.40 272-280 Aluminum oxide, phosphoric acid treated" 6 511 31- 32 98. 42 225 Thorium oxide, 10% on support 63 254 30.94 99.27 276 l 4 x 6 mesh c'eramlcally bonded fused aluminum oxide.

I Grams of styrene per liter of catalyst per hour.

Similar data on runs using a number of additional materials as catalysts in the vapor phase dehydration reaction are listed in Table 3.

actual efllcieucy on the basis of styrene recovered was 94.7 percent while the efficiency loss due to dimer formation was 2.78 per cent.

Table B Produc- Btyrene Reaction Description of material tion freezing tempers.

ratio l point p ture Alumina activated with per cent sulfuric or phosphoric C. 1 Per cent 0.

acid: 611 3l2l4m to 98.47 to 98.67 226 Silica gelen --31. e1 e7. 72 22s Thorium oxide, 10% on support I 254 30. 96 99. 22 275 Cerium oxide, 10% on support 171 275 Sodium bisuliate, 157 ou'suppoi't 666 -30.85 99.47 226 Sodium dihydrogen phosphate, on support 1 500 250-275 Magnesium pyropbosphate, pellets 650-700 -3l 28 to 98. 51 t099. 22 276 Calcium sulfate, 10% on support 1 249 -z1.'43 as is m Potassium dihydrogen phosphate, 16% on support 280 276 Potassium phosphate, 16% on support 0 275 l Ceramically bonded, fused aluminum oxide. I Grams of styrene per liter of catalyst per hour.

In determining the purity of the styrene pro- Example 2 duced, its freezing point was measured by resistance thermometry, the impurity present therein being calculated as ethyl benzene. For this purpose, -30.61 C. was taken as the melting point of pure styrene, and 2.22 per cent as the amount of ethyl'benzene which lowers the freezing point 1.0 C. (a'lowering of 0.44 C. for each mole per the Bureau of Standards. The sensitivity of the resistance thermometer used was such that a change in resistance of 0.0001 ohm, corresponding to a change of 0.001 C., was measureable. Due to other variables, however, the precision is estimated as being not better than :0.005 C.

The following examples are illustrative of the invention:

Example 1 A mixture containing 80.3 per cent phenyl methyl carbinol and 19.7 per cent acetophenone was vaporized and the vapor passed through a catalyst bed maintained at a temperature of 250 C. The catalyst was titania supported on 4 x 6 mesh, ceramically-bonded. fused aluminum oxide.

' cent of impurity). according to values reported by The catalyst was prepared by sprinkling 15 parts yield of products was as follows:

Per cent Styrene 82.6 Dimer 2.48 Ether 2.78 Carbinol, unreacted 10.03 Loss 2.11

The percentage dehydration of the carbinol, as measured by the water produced was 85.2 per cent. The production ratio of styrene was 460 grams per liter per hour and the overall purity of the styrene produced was 99.71 per cent as indie cated by its freezing point of --30.74' C. The

The re- In this run the chemically pure anhydrous grade titania was treated with hot aqueous sulfuricacid of 10 per cent concentration and washed thoroughly before being put on the aluminum oxide support. The feed was a mixture containing 87.7 per cent phenyl methylcarbinol and 12.2 per cent acetophenone by weight. In other respects the apparatus was identical with that described in Example 1. The temperature was maintained at 250 C., and the mixture was vaporized and supplied to the catalyst bed at such a rate that 1025 grams were fed over a period of 4.5 hours.

The percentage dehydration, as shown by the water produced, was 98.2 per cent. The production ratio was 574 grams of styrene per liter of catalyst per hour and the overall purity of the styrene produced was 99.58 per cent as-indicated by its freezing point of -30.80 C. The yield of styrene was 92.2 per cent and the efficiency 92.2 per cent. Th loss of efficiency attributable to dimer formation was 5.8 per cent.

Example 3 A mixture containing 79.4 per cent phenyl methyl carbinol and 20.6 per cent acetophenone was vaporized and the vapor passed into a bed of pelleted titania catalyst maintained at a temperatureof 250 C. The catalyst was prepared by thoroughly wetting titanium dioxide powder of a chemically pure anhydrous grade with water and drying the resultant paste at a temperature of C. to C. After the dried cake had been powdered, the powder was formed into pellets of fir inch diameter x inch, and the pellets then fired or roasted in an electric furnace at a temperature of 800 0. Finally the pellets which were strong and very suitable mechanically, were treated by immersion in boiling aqueous nitric acid of 18 to 20 per cent concentration for a period of 1.5 hours, as an activation step. At the end of that time the pellets were washed with water thoroughly, dried at 130 to 150 C. and charged into a steel tube having an inside diameter of one inch. The length of the catalyst bed was 4.6 ft., corresponding to a catalyst volume of 0.0318 cubic it. (900 cubic centimeters). The feed was maintained at such a rate that 97.6 pounds of mixture were supplied to the converted over a period or eight hours.

The yield of styrene was 82.5 per cent, and the eiiiciency was 90.2 per cent. The loss of eiflciency due to dimer formation was 9.2 per cent. The production ratio was 214.5 pounds or styrene per cubic foot of catalyst per hour (3440 grams per liter per hour); The purity of the styrene produced was 99.53 per cent as indicated by its freezing point of 30.82 C.

Example 4 During a period of 3.33 hours, 1020 grams of a mixture containing 75.6 per cent phenyl methyl carbinol and 24.4 per cent acetophenone were vaporized and the vapor passed into contact with 168.5 cubic centimeters of pelleted titania catalyst. The pellets which were 1"; inch in diameter x inch were made as described in Example 3 but activated by boiling the catalyst pellets in aqueous.

hydrochloric acid of 20 per cent concentration, instead or in aqueous nitric acid. Thecatalyst was packed in a steel tube of 1 inch inside diameter provided with a concentric tube of flinch outside diameter serving as a. thermometer well, as described in Example 1. The temperature of the catalyst bed was maintained at 250 C. The yield of styrene was 79.4 per cent and the production ratio was 860 grams of styrene per liter of catalyst per hour. The freezing point of the styrene produced was 30.77 C., corresponding to an indicated purity of 99.64 per cent.

Example 5 The average yield as determined by the specific gravity of the product was 65.2 per cent. After 20 hours of operation, the water feed was discontinued without any other change in operating conditions. The yield rose to 85.0 per cent for the succeeding 175 hours of operation. Throughout the run the reaction temperature was maintained at 240 C.

The invention is susceptible of modification within the scope of the appended claims.

What is claimed is:

1. A method 01' making styrene which comprises passing phenyl methyl carbine] in the vapor phase over a titania catalyst at a temperature sufllciently elevated to cause dehydration of the phenyl methyl carbinol.

2. A method of making styrene which comprises passing phenyl methyl carbinol in the vapor phase over a titania catalyst at a temperature from about to 280 C.

3. A method of making styrene which comprises passing phenyl methyl carbinol in the vapor phase over a titania catalyst at a temperature *from about 220 to 250 C.

4. A method of making styrene which comprises passing phenyl methyl carbinol in the vapor phase over a titania catalyst which has been brought into contact with strong mineral acid to activate it 5. A method of making styrene which comprises passing phenyl methyl carbinol over a pelleted titania catalyst.

6. A method of making styrene which comprises passing phenyl methyl carbinol over a mechanically strong, pelleted titania catalyst, fired at a temperature from about 800 to 1100 C. after pelleting, and thereafter brought into contact with hot mineralacid to activate the catalyst pellets.

7. A method of making styrene which comprises passing phenyl methyl carbinol in admixture with water in the vapor phase over a mechanically strong, pelleted titania catalyst fired at a temperature from about 800 to 1100 "C. after pelleting and thereafter brought into contactv with strong mineral acid to activate the catalyst pellet.

8. A method of making styrene which comprises passing phenyl methyl carbinol in the vapor phase over a mechanically strong, pelleted titania catalyst having a pellet size not substantially greater than 1"; inch, at a temperature from about 220 to 280 C.

9. A method 0! making styrene which comprises passing phenyl methyl carbinol in the vapor phase over a mechanically strong, pelleted titania catalyst having a pellet size not substantially greater than inch in the longest pellet dimension and fired at a temperature of about 1000 C. and thereafter brought into contact with strong mineral acid to activate the catalyst pellet, at a temperature from about 220 to 250 C.

LELAND C. SHRIVER. 

